This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-253360, filed Aug. 23, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical deflector with an oscillating member prepared by the semiconductor manufacturing technique, and in particularly, to an optical deflector of the electromagnetic driving type.
2. Description of the Related Art
As an optical deflector prepared by the semiconductor manufacturing technique, there has heretofore been a planar electromagnetic actuator disclosed in U.S. Pat. No. 5,912,608. The planar electromagnetic actuator comprises: a structure member integrally formed by a frame-shaped outer movable portion, an inner movable portion positioned inside the outer movable portion, a first torsion bar for supporting the outer movable portion so as to allow the outer movable portion to oscillate, and a second torsion bar for supporting the inner movable portion with respect to the outer movable portion so as to allow the inner movable portion to oscillate; and two permanent magnets disposed on opposite sides of the structure member.
The first torsion bar crosses at right angles to the second torsion bar, and the inner movable portion is, therefore, allowed to oscillate about two axes crossing at right angles to each other. The outer and inner movable portions include electromagnetic coils. Two permanent magnets are arranged on a diagonal line of the movable portion, in other words, on a line obliquely intersecting with any one of two oscillation axes.
In the actuator or optical deflector of the electromagnetic driving type, a current flowing through the electromagnetic coil disposed in the movable portion receives Lorentz force by an interaction with a magnetic field crossing at right angles to the oscillation axis of the movable portion. Thereby, the movable portion is oscillated. Therefore, each permanent magnet is usually disposed in the vicinity of each side of the movable portion, that is, four permanent magnets are arranged in total for a two-dimensional driving.
In the electromagnetic actuator described in the above-described patent, the magnetic field obliquely crossing two oscillation axes of the movable portion is generated by only the two permanent magnets generate. The magnetic field can be split into two components crossing at right angles to two oscillation axes. By the Lorentz force generated by the interaction of two magnetic field components with the current flowing through the electromagnetic coil of the inner or outer movable portion, the inner movable portion is allowed to oscillate about two axes crossing at right angles to each other.
Not only in the above-described planar electromagnetic actuator (optical deflector) but also in the electromagnetic driving type of actuator (optical deflector) that has heretofore been known, the permanent magnets are disposed beside the movable portion. Therefore, in an optical deflector of the electromagnetic driving type of optical deflector constituted by mounting a mirror on the movable portion of the actuator, the permanent magnet projects forwards from at least the mirror. Therefore, a beam of light incident upon the mirror at a small angle, in other words, a beam of light incident with a large incidence angle is diverted by the permanent magnet, and a situation in which the deflector cannot accurately function possibly occurs.
Moreover, since the permanent magnet is disposed beside the movable portion, an area occupied by the electromagnetic driving type of actuator is very large in a projection onto a surface parallel to the surface of the movable portion in a neutral position. Here, the movable portion in the neutral position is a movable portion which is not oscillated/dislocated. Such an actuator or optical deflector of the electromagnetic driving type is not suitable for an endoscope. That is, it is difficult to dispose an actuator or optical deflector of the electromagnetic driving type, which includes the permanent magnet disposed beside the movable portion, in a narrow space of an endoscope tip end having a small diameter.
An optical deflector according to the present invention comprises: an oscillating member including at least one movable plate allowed to oscillate in at least one dimension, the movable plate including a coil extending along the periphery of the movable plate; and a magnetic field generation portion, which generates a magnetic field, such that the movable plate oscillates in accordance with a force generated by an interaction of a current flowing through the coil with the magnetic field generated by the magnetic field generation portion, wherein the movable plate has first and second surfaces forming front and back surfaces, respectively, and extending in substantially parallel with each other, an imaginary plane including the first surface of the movable plate in a neutral position defines two spaces, one including the second surface of the movable plate and the other not including the second surface, and the magnetic field generation portion is positioned in the space including the second surface of the movable plate.
More preferably, an imaginary plane including the second surface of the movable plate in a neutral position defines two spaces, one including the first surface of the movable plate and the other not including the first surface, and the magnetic field generation portion is positioned in the space not including the first surface of the movable plate. Furthermore, in a projection onto an imaginary plane parallel to the first surface of the movable plate in the neutral position, preferably, the magnetic field generation portion and oscillating member at least partially overlap with each other, and more preferably, the magnetic field generation portion is positioned inside a contour of the oscillating member.
According to the present invention, there is provided an electromagnetic driving type optical deflector in which a beam of light incident upon a movable plate is not diverted by permanent magnets. Since the optical deflector according to the present invention has a small occupying area in a projection onto a plane parallel to the surface of the movable plate in the neutral position, the optical deflector is suitable for incorporation into an endoscope tip end.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.